Mental health professionals are eagerly awaiting the Clinton administration's health-care reform proposal. For the first time in history, they see a chance that mental illness will get the same insurance coverage as physical illnesses. For the 5 million Americans who suffer from severe mental disorders, such as schizophrenia and major depression, that could mean affordable access to drugs and treatments that have dramatically improved in recent years. But the business community has voiced concern about the high cost of parity, and a split has opened between advocates for the severely mentally ill and those who would also cover less serious psychological complaints. A diverse field of psychiatrists, psychologists, academics and community health specialists are struggling for unity on the issue.